Readily strippable cable

ABSTRACT

A cable having conductors that may be easily exposed in preparation for electrical connection, without requiring the use of tools, is provided. The insulating layer of the cable has at least one relatively weak portion extending along the length of the cable that is configured to allow the insulating layer to split, thereby exposing the wire without the use of tools.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/070,161, filed Aug. 18, 2014. This application is herein incorporatedby reference in its entirety for all purposes.

FIELD OF THE INVENTION

The invention relates to electrical cables, and more particularly, toreadily strippable cables particularly suited for use in ductlessmini-split AC systems.

BACKGROUND OF THE INVENTION

Existing electrical wires and cable and their associated methods ofinstallation require the use of tools, such as wire strippers andcutters, to expose the conductive elements of the wires in preparationfor their connection to an electrical system. This process takes bothtime and skill and can be time consuming, even for experiencedinstallers, especially when the time consumed is considered over thecourse of a project. Errors during this operation may also result in theinsulation surrounding the conductor being compromised or the wire beingsevered, requiring additional time to be spent on repair before the workcan proceed.

In addition to time and skill requirements, this seemingly simple taskalso occasionally results in workplace injuries. This is, in part,because the preferred industry tool for stripping such a cable is autility knife. According to the Massachusetts governmental website, thesecond most likely reason for an 18-24 year old male to visit theemergency room with a work related injury is being cut or pierced.Notably, 15,154 or 28.1% of visits in Massachusetts emergency roomsresult from such injuries annually in Massachusetts alone. Nationally,emergency rooms treat over 750,000 patients annually with work-relatedcut or pierce injuries. A wire that omitted the use of a utility knifefrom the stripping operation would inevitably lead to a reduction insuch injuries and would help to save millions of dollars annually.

Cables, which contain a plurality of individually-sheathed wires,present an even larger challenge to installers and a significantlylarger risk of costly and/or time consuming errors being made. Withcables, the outer sheathing must be cut away to expose the jacketing ofindividual wires for stripping, further increasing the time anelectrician, HVAC tech, professional installer, homeowner or otherperson installing the wiring must spend preparing the wires forinstallation and the risk of damage to the underlying conductor fromaccidental puncture of the protective jacket during sheathing removal.

A somewhat related problem involves ductless mini-split A/C systems. Inrecent years, mini-split ductless AC systems have become popular. Thesesystems are similar to traditional central air conditioning systems inthat they locate the noisiest part of the system, the compressor andassociated hardware, outdoors. Such systems, however, do not requireextensive ductwork to be installed within the home, thus making them areasonable and cost-effective upgrade to an existing structure.

While the systems themselves are relatively easy to install, relative totraditional centralized air conditioning systems, the cabling for suchsystems is relatively complicated, requiring AC power wires, DC signalor communications conductors and non-current carrying ground wires tofunction, each of which must be separated by sheathing in addition tothat of the individual wires. There is currently no cable that canprovide ease of use, durability and the required connectors forinstallation of such a system, while meeting code requirements.

What is needed, therefore, are wires and cables that do not require theuse of tools to expose the conductors within, enabling their tool-lessinstallation, particularly wires and cables suitable for use in theinstallation of mini-split ductless AC systems.

SUMMARY OF THE INVENTION

One embodiment of the present invention provides a readily-strippablecable comprising: at least two wires encapsulated by a continuouselectrically insulating layer wherein each encapsulated wire isconnected to an adjacent wire by a relatively thinner portion of theinsulating layer, the insulating layer having at least one relativelyweak portion per encapsulated wire that extends along the length of thecable and is substantially uniform in position and strength along thelength of the cable; and wherein the weak portion is configured to allowthe insulating layer to split along the relatively weak portion and downthe length of the cable upon separation of encapsulated wires byapplication of force against the relatively thinner portion ofinsulating layer in a direction substantially perpendicular to thelength of the cable, thereby exposing the wire without the use of asecondary operation.

Another embodiment of the present invention provides such a cablewherein the relatively weak portion is positioned adjacent each therelatively thinner portion of the insulating layer connecting adjacentwires.

A further embodiment of the present invention provides such a cablewherein no wire is present in the relatively thinner portion of theinsulating layer connecting adjacent wires.

Yet another embodiment of the present invention provides such a cablewherein at least one of the encapsulated wires is jacketed.

A yet further embodiment of the present invention provides such a cablewherein the wire jacket of the at least one jacketed inner wire has atleast one relatively weak portion that extends along the length of thewire jacket and is substantially uniform in position and strength alongthe length of the wire jacket; and wherein the relatively weak portionis configured to allow the insulating layer to split along therelatively weak portion and down the length of the wire jacket uponseparation of the encapsulated wires by application of force against therelatively thinner portion of insulating layer in a directionsubstantially perpendicular to the length of the cable, thereby exposingthe wire without the use of a secondary operation.

Still another embodiment of the present invention provides such a cablewherein the wire jacket is configured to adhere to the insulating layerof the cable.

A still further embodiment of the present invention provides such acable wherein the relatively weak portions of the wire jacket and theinsulating layer are adjacent one another.

Even another embodiment of the present invention provides such a cablewherein the relatively weak portion is a knit line created duringextrusion of the cable.

An even further embodiment of the present invention provides such acable wherein the relatively weak portion is a knit line created duringextrusion of the cable.

A still even another embodiment of the present invention provides such acable wherein the insulating layer is made of a foamed polymer.

A still even further embodiment of the present invention provides such acable wherein the foamed polymer is a closed-cell foam polymer.

Still yet another embodiment of the present invention provides such acable wherein the foamed polymer is an open cell foam polymer.

A still yet further embodiment of the present invention provides such acable wherein the cable is rated for direct-burial.

Even yet another embodiment of the present invention provides such acable wherein the at least two wires consist of two AC power wires, a DCsignal wire, and a non-current carrying ground wire.

An even yet further embodiment of the present invention provides such acable wherein the two AC power wires and the DC signal wire are strandedconductors and the non-current carrying ground wire is a solidconductor.

Still even yet another embodiment of the present invention provides sucha cable wherein the cable is a UF-B cable.

One embodiment of the present invention provides a method ofmanufacturing readily-strippable cable comprising: configuring anextrusion die to separate a polymer flow into at least two separatepolymer flows; attaching the extrusion die to an extruder; adjustingprocessing parameters and tooling configuration to cause the polymerflows, during extrusion, to meet when they are relatively cold and underrelatively low pressure, thereby creating a uniformly weak portion thatextends along the length of the cable to be formed; introducing at leasttwo wires to be made into a readily-strippable cable into the extrusiondie for coating with the polymer, wherein the wires are separated fromone another; and operating the extruder, thereby creating areadily-strippable cable.

Another embodiment of the present invention provides such a methodwherein the extrusion die is a crosshead die.

A further embodiment of the present invention provides such a methodwherein the processing parameters and tooling configurations comprise:extrudate temp; compound pressure at tip/die; tip/die temperatures;cooling effects; tool design/construction, including tooling tip wallthickness and hole sizes relative to wire size; vacuum or pressure atdie; incoming wire temperature; head tip and die temps, including aircooling or heating of tooling tips from the back of the head and theamount of contact with wires of the tooling tip; crosshead design; andcompound type, including the presence of color concentrates.

Yet another embodiment of the present invention provides such a methodwherein tubing-style tooling is used in conjunction with vacuum, whereinthe vacuum is used to pull the extrudate onto the wire(s).

The features and advantages described herein are not all-inclusive and,in particular, many additional features and advantages will be apparentto one of ordinary skill in the art in view of the drawings,specification, and claims. Moreover, it should be noted that thelanguage used in the specification has been principally selected forreadability and instructional purposes, and not to limit the scope ofthe inventive subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front-elevation sectional view of a four-wire cable havingan offset ground wire sheathing configured in accordance with oneembodiment of the present invention;

FIG. 2 is a front-elevation sectional view of a four-wire cable having aground wire offset in its sheathing configured in accordance with oneembodiment of the present invention;

FIG. 3 is a front-elevation sectional view of a four-wire cable havingan offset ground wire sheathing and knit lines in both the cablesheathing and wire jackets configured in accordance with one embodimentof the present invention;

FIG. 4 is a front-elevation sectional view of a four-wire cable having aground wire offset in its sheathing and knit lines through both thecable sheathing and wire jackets configured in accordance with oneembodiment of the present invention;

FIG. 5 is a front-elevation sectional view of a neutral wire portion ofa cable wherein the ground wire is centered within cable sheathing thatis centered within webbing between adjacent cables (not shown);

FIG. 6 is a front-elevation sectional view of a neutral wire portion ofa cable wherein the ground wire is offset within cable sheathing that iscentered within webbing between adjacent cables (not shown); and

FIG. 7 is a front-elevation sectional view of a neutral wire portion ofa cable wherein the ground wire is offset within cable sheathing that isoffset within webbing between adjacent cables (not shown).

DETAILED DESCRIPTION

The invention is susceptible of many embodiments and variations. What isdescribed here is illustrative, but not limiting, of the scope of theinvention.

Referring to FIG. 1, a front-elevation sectional view of a four-wirecable 100 having an offset ground wire 102, or bonding conductor 102 (aninsulated or uninsulated conductor forming part of the cable 100assembly which is used for the purpose of connecting non-currentcarrying parts of electrical equipment to a system grounding conductor),cable sheathing 104 and wire jacketing 106 configured in accordance withone embodiment of the present invention is shown. More specifically, thecable 100 shown comprises: multiple wire cores 108, the portions ofinsulated wires, which may be stranded and/or solid conductors, lyingunder a protective covering 106, the wire jacketing 106; a cable sheath104, the overall protective covering applied to the cable 100; a bondingconductor 102; and wire jacketing 106, which encapsulates at least someof the wire cores 108.

In embodiments, the cable 100 may beneficially be a buried cable 100; acable 100 installed directly in the earth without use of undergroundround conduit, also called a direct burial cable 100, and should havereasonable cut-through resistance, the ability of a material towithstand mechanical pressure, usually a sharp edge of prescribedradius, without separation. The cable sheath 104, in embodiments, may bemade of a foamed plastic, i.e. plastic having a cellular structure,whether open or closed.

The cable 100 described above may generally be referred to as a bondedflat cable 100, which comprises individually insulated conductors 108,or wire cores 108, lying substantially parallel to one another andbonded together. The cable sheathing 104 connecting adjacent wire cores108 is referred to as cable webbing 112 Such a cable 100 has numerousapplications in electronics, telecommunications, computing andconstruction. This type of cable 100 is typically manufactured throughan extrusion process, where a plastic or elastomeric material and atleast two wire cores 108, which may or may not have wire jacketing 106,are forced through an extrusion die, typically a cross-head die, at acontrolled rate, thereby imparting a continuous coating of insulation106 or jacketing 106 to wires 108 to be contained therein. The wires 108themselves are also often formed in a similar manner. The extrusionprocess sometimes results in so-called “knit lines” 110 in the finalmaterials.

A knit line 110 is created where two or more flow fronts meet when thereis the inability of the two or more flow fronts to “knit” together, or“weld”, during the extrusion process. These lines cause locally weakareas in the extruded part and are normally considered defects. Theygenerally occur when the die and/or material temperatures are set toolow, resulting in the materials being relatively cold upon meeting, suchthat they do not bond perfectly. Such “defects” are also sometimesreferred to as weld or meld lines 110.

Knit lines 110 are created in cross-head dies because the compound flowis separated in such designs—usually top and bottom—so the compound canbe diverted to ‘surround’ the wire core 108 or wire jacketing 106, asnecessary. The compound flows, following separation, are subsequentlyrejoined via the crosshead design. If the compound is too cool when theseparate flows re-join, the compound from the different flow paths willnot adhere sufficiently to form a uniform layer over the wire core 108or wire jacket 106. Similarly, when the knit lines are too loose, thejacketing may not be retained on the wires, while if it is too tight itmay not readily strip. Suffice it to say that carefully controlledmanufacturing processes are required for knit lines to serve theirintended purpose. A non-exhaustive list of key factors that define knitline 110 properties, such as strength and uniformity, include: extrudatetemp; compound pressure at tip/die; tip/die temperatures; and coolingeffects. Other notable factors include: tool design/construction,including tooling tip wall thickness and hole sizes relative to wiresize; vacuum or pressure at die; incoming wire temperature; head tip anddie temps, including air cooling or heating of tooling tips from theback of the head and the amount of contact with wires of the toolingtip; crosshead design; and compound type, including the presence ofcolor concentrates.

Now referring specifically to tooling type, there are two primarydesigns used, namely: “pressure” and “tubing” style tooling. Pressuretooling will generally utilize a relatively sharp angle, as compared totubing type tooling, where the compound flows around the tip of thetooling and into the die. This design allows high pressure in theextruder to force the extrudate around the wire before being shaped bythe die. Tubing' style tooling has a relatively longer tip thatgenerally extends into the die and typically the compound is at a muchlower pressure as it is formed around the wire(s). Tubing style toolingmay even require a vacuum to be applied to pull the extrudate onto thewire(s).

There are many variations on pressure and tubing style tooling, withsome designs being deliberate hybrids of the two concepts. Complexshapes may even combine elements of the designs within the same tooling.Practically speaking, tubing style tooling tends to allow knit lines toform more easily while pressure style tooling tends to prevent orminimize the formation of knit lines. It is also possible to adjusteither design during processing by moving the die in relation to thetooling tip. This change slightly affects the amount of pressure ortubing characteristics of the setup. This adjustment can be a way tofinely adjust the knit line without resorting to new tooling.

When using either style of tooling, vacuum or positive pressure can beapplied to the die to help the extrudate more tightly form to the wires.Vacuum is more common when tubing style tooling is used to pull theextrudate to the wire more tightly and can be used to control the sizeand uniformity of the knit line on a flat cable construction by pullingthe layers more firmly together.

Through careful configuration and control of wire and cable 100processing conditions, it was found that wires and cables 100 havingpredictable and uniform knit lines 110 may be created. Although knitlines 110 are usually undesirable, especially when applying aninsulation layer, or protective covering, over cables 100, when takenadvantage of, as is taught by the current disclosure, correctlypositioned and consistent knit lines 110 allow the creation of a cable100 having key advantages over those of the prior art.

Of particular note to the current disclosure, the cable 100 of FIGS. 1-4makes novel use of knit lines 110 to allow the cable 100 to be safelyand easily stripped in the field, without the use of tools and withoutsacrificing cable sheathing 104 strength under normal use. Inembodiments, as shown in FIGS. 1-4, knit lines 110 may beneficially bepositioned proximal to the webbing 112 between adjacent wire cores 108or wire jacketing 106, if used.

When individual wires within such a cable 100 are separated by theexertion of force applied perpendicularly to the length of the cable100, against the cable 100 webbing 112 connecting adjacent wires, thepresence of knit lines 110 adjacent to this webbing 112 causes the cablesheathing 104 to split. This split results in the cable sheathing 104readily detaching from the wire jacket 106 or wire core 108 containedwithin upon further exertion of force, obviating the need for asecondary operation to remove the cable sheathing 104 following wireseparation.

Now referring to FIGS. 3 and 4, embodiments of the present invention areshown that make use of cables 100 containing jacketed wires 106 havinguniform knit lines 110. The uniform wire jacket 106 knit lines 110 allowfor a further step in the forming of electrical connections, namelystripping of the wire jacket 106 from the wire core 108, to be performedautomatically as the wires contained within the cable 100 are separated.In this design, the cable 100 is separated into individual wire segmentsby the exertion of force perpendicularly to the lengthwise direction ofthe cable 100 against the cable webbing 112 connecting adjacent wires inthe same way as the previous embodiment. Upon separation of the cable100 into its component wires, the inner wire jacket 106 knit lines 112cause the wire jacketing 106, in addition to the cable sheathing 104, tosplit, allowing it to be quickly and easily removed by an installer,without the use of tools. In embodiments, the wire jacket 106 knit lines110 may be substantially aligned with those of the cable sheathing 104.

The use of stranded and/or solid conductors as wire cores 108, differentnumbers of wires, different shapes of cable 100 and other variations arewithin the scope of the current disclosure. Furthermore, embodiments ofthe present invention make use of: a ground wire 102 cable sheathing 104that is offset from a plane defined by other wires in the cable 100, asshown in FIGS. 1, 3 and 7; a ground wire 102 that is offset within cablesheathing 104 that is otherwise within a plane defined by other wireswithin the cable 100, as shown in FIGS. 2, 4 and 6; and a ground wire102 and cable sheathing 104 that is within the plane defined by otherwires in the cable, as shown in FIG. 5. The wire core 108 eccentricity,a measure of the displacement of the center of the wire core 108relative to the center of the cable sheathing 104, of the other wireswithin the cable 100 as well as the particular gauges of wire used mayalso change without departing from the scope of the current disclosure.

Additional embodiments particularly suited for use in ductlessmini-split air conditioning systems may include an AC power wire, a DCpower wire, a ground wire 102 offset from a plane defined by the otherwire cores 108 and a signal wire. In such an embodiment, the cable 100may also beneficially be rated as a direct-buried cable.

The foregoing description of the embodiments of the invention has beenpresented for the purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdisclosed. Many modifications and variations are possible in light ofthis disclosure. It is intended that the scope of the invention belimited not by this detailed description, but rather by the claimsappended hereto.

What is claimed is:
 1. A readily-strippable cable comprising: at leasttwo wires encapsulated by a continuous electrically insulating layerwherein each encapsulated wire is connected to an adjacent wire by arelatively thinner portion of said insulating layer, said insulatinglayer having at least one relatively weak portion per encapsulated wirein at least one cross-sectional segment of said continuous electricallyinsulating layer that is substantially concentric with at least one wireand that extends along the length of the cable and is substantiallyuniform in position and strength along the length of said cable; andwherein said weak portion is configured to allow the insulating layer tosplit along the relatively weak portion and down the length of saidcable upon separation of encapsulated wires by application of forceagainst said relatively thinner portion of insulating layer in adirection substantially perpendicular to the length of said cable,thereby separating said wires from one another and simultaneouslyseparating the insulating layer from said wire, without the use of asecondary operation.
 2. The cable of claim 1 wherein said relativelyweak portion is positioned adjacent each said relatively thinner portionof said insulating layer connecting adjacent wires.
 3. The cable ofclaim 1 wherein no wire is present in said relatively thinner portion ofsaid insulating layer connecting adjacent wires.
 4. The cable of claim 1wherein at least one of said encapsulated wires is jacketed.
 5. Thecable of claim 4 wherein said wire jacket of said at least one jacketedinner wire has at least one relatively weak portion that extends alongthe length of said wire jacket and is substantially uniform in positionand strength along the length of said wire jacket; and wherein saidrelatively weak portion is configured to allow the insulating layer tosplit along the relatively weak portion and down the length of said wirejacket upon separation of said encapsulated wires by application offorce against said relatively thinner portion of insulating layer in adirection substantially perpendicular to the length of said cable,thereby exposing said wire without the use of a secondary operation. 6.The cable of claim 5 wherein said wire jacket is configured to adhere tosaid insulating layer of said cable, thereby allowing the wire to bestripped from the cable and the conductor to be stripped from the wirein a single, tool-less step.
 7. The cable of claim 5 wherein saidrelatively weak portions of said wire jacket and said insulating layerare adjacent one another.
 8. The cable of claim 5 wherein saidrelatively weak portion is a knit line created during extrusion of saidcable.
 9. The cable of claim 1 wherein said relatively weak portion is aknit line created during extrusion of said cable.
 10. The cable of claim1 wherein said insulating layer is made of a foamed polymer.
 11. Thecable of claim 10 wherein said foamed polymer is a closed-cell foampolymer.
 12. The cable of claim 10 wherein said foamed polymer is anopen cell foam polymer.
 13. The cable of claim 1 wherein said cable israted for direct-burial.
 14. The cable of claim 1 wherein said at leasttwo wires consist of two AC power wires, a DC signal wire, and anon-current carrying ground wire.
 15. The cable of claim 14 wherein saidtwo AC power wires and said DC signal wire are stranded conductors andsaid non-current carrying wire is a solid conductor.
 16. The cable ofclaim 1 wherein said cable is a UF-B cable.
 17. A method ofmanufacturing readily-strippable cable comprising: configuring anextrusion die to separate a polymer flow into at least two separatepolymer flows; attaching said extrusion die to an extruder; introducingat least two wires to be made into a readily-strippable cable into saidextrusion die for coating with said polymer, wherein said wires areseparated from one another; adjusting processing parameters and toolingconfiguration to cause said polymer flows, during extrusion, to meetwhen they are relatively cold and under relatively low pressure, therebycreating a uniformly weak portion in at least one cross-sectionalsegment of the polymer coating concentric with and surrounding at leastone wire and that extends along the length of said cable to be formed;and operating said extruder, thereby creating a readily-strippablecable.
 18. The method of claim 17 wherein said extrusion die is acrosshead die.
 19. The method of claim 18 wherein said processingparameters and tooling configurations comprise: extrudate temp; compoundpressure at tip/die; tip/die temperatures; cooling effects; tooldesign/construction, including tooling tip wall thickness and hole sizesrelative to wire size; vacuum or pressure at die; incoming wiretemperature; head tip and die temps, including air cooling or heating oftooling tips from the back of the head and the amount of contact withwires of the tooling tip; crosshead design; and compound type, includingthe presence of color concentrates.
 20. The method of claim 17 whereintubing-style tooling is used in conjunction with vacuum, wherein saidvacuum is used to pull the extrudate onto the wire(s).